First Bell test of massive-particle momentum entanglement

Metastable helium-4 BEC · Rarity-Tapster interferometer · s-wave scattering halos
BEC Formation
~100,000 metastable helium-4 atoms cooled to quantum degeneracy. A single macroscopic quantum state.
Based on: Bell correlations between momentum-entangled pairs of ⁴He* atoms, Nature Communications 17, 2357 (2026)

Bell Correlation E(φ)

3.9σ VIOLATION

Controls

Momentum-entangled atom pairs violate Bell's inequality,
confirming quantum correlations in massive particles.
3.9σ violation of classical bound |E| ≤ 1/√2